The acute chest syndrome is initiated by lung inflammation that induces increased adhesion of sickled red[unreadable] blood cells to pulmonary microvascular endothelium. Emerging evidence indicates the interaction between[unreadable] red blood cells and endothelium is dynamic. While in the non-inflamed state perfusion is facilitated by antiadhesive[unreadable] proteins expressed on the endothelial surface, in the inflamed state vaso-occlusion is partly caused[unreadable] by upregulation of adhesive proteins such as P-selectin and release of von Willebrand factor (vWf) from[unreadable] microvascular endothelium. The secretory organelle in endothelium is the endothelial cell specific organelle[unreadable] called Weibel-Palade body. In the inflamed circulation thrombin and other Gq-linked neurohumoral[unreadable] inflammatory mediators increase endothelial cell cytosolic calcium, and this rise in cytosolic calcium is[unreadable] sufficient to cause rapid translocation of Weibel-Palade bodies to the plasmalemma for vWf secretion and P-selectin[unreadable] up-regulation. Specific calcium entry pathways that stimulate vWf secretion and P-selectin upregulation[unreadable] remain incompletely understood, particularly in microvascular endothelial cells obtained from the[unreadable] prominent site of vaso-occlusion. Preliminary studies suggest that lung microvascular endothelial cells[unreadable] expess T-type, voltage-activated calcium channels which promote a pro-coagulant endothelial phenotype[unreadable] during inflammation. In this proposal, we will test the overall HYPOTHESIS that calcium entry through T-type[unreadable] calcium channels is an important amplification step in release of vWf and up-regulation of P-selectin from[unreadable] lung microvascular endothelium that promotes the retention of sickled red blood cells. The hypothesis will be[unreadable] explored using lung microvascular endothelial cells in culture and an isolated rat lung model, in which the[unreadable] role of the T channel to red blood cell retention can be assessed under flow conditions. The SPECIFIC AIMS[unreadable] test the hypotheses that: [1] Lung microvascular endothelial cells express a T-type calcium channel that is[unreadable] activated by Gq-linked neurohumoral inflammatory mediators, and [2] Activation of T-type calcium channels[unreadable] promotes the release of vWf and up-regulation of P-selectin from lung microvascular endothelial cells[unreadable] important for vaso-occlusion. It is hoped completion of these studies will improve our understanding of[unreadable] mechanisms that regulate erythrocyte-endothelial adherence so that effective therapies can be developed for[unreadable] treatment of sickle cell anemia, as well as other vascular thrombosis disorders.